It is necessary to evaluate doses of nuclear particles in several applications and in particular to assess the risks run by living beings to be accurately evaluated by what is called a dose equivalent, that is the sum of the doses of particles of each species weighted by multiplier coefficients (quality factors).
An example of a dose rate meter is described in the preceding French patent of the same inventors (FR-A-2 645 652). It includes two semiconductor diodes each delivering a signal on an electric circuit. This signal is proportional to the dose equivalent flow rate of the particles which reach the diode. The characteristic feature of this prior device consists in that one of the diodes is covered by a hydrogenated screen which reacts with the neutrons so that it solely is sensitive to the neutrons and photons. The measurements consist of subtracting from the signal of this diode that of the other so as to obtain the dose flow rate associated with the single neutrons of the radiation.
There are two criticisms regarding this device: the influence of the photonic radiation (X-rays or .gamma.-rays), which comprises the real mixed radiation, is ignored, although its effects may be quite considerable in practice, and in particular the diodes are always different, irrespective of the production precautions taken, and have different sensitivities. The result may thus contain a large number of errors.
There also exist portable dose rate meters (for example in U.S. Pat. No. 4 489 315) which separately measure the flow rates of the two different categories of neutrons so as to evaluate the equivalent of the dose by means of a weighting. These devices are subject to the same drawbacks, namely of ignoring the flow rate of the .gamma. rays and of using two separate detectors.